Hi,
Thank you for posting in Symantec community.
I would be glad to answer your query.
You must be knowing however on January 5th, 2015, Symantec Endpoint Protection version 11.0.x reached end of support life. Virus definitions and security updates ceased to be published to LiveUpdate and general support for the product is no longer provided.
The initial end of support life date was originally scheduled for January 5th, 2014. All customers were provided a complimentary extention. No further extentions will be provided.
It's strongly recommended to upgrade to SEP 12.1, RU5 is the latest release.
Upgrade from 11.0.5002.333 (RU5) to SEP 12.1.5337.5000 (RU5) is fully supported.
Q. Prerequisites?
1) Create an upgrade plan
3) Back up and prepare for disaster recovery (critical)
3) Prepare Symantec Endpoint Protection 11.x managers.
- Disable replication
- Disable the "Protect client files and registry keys" Application Control Policy
- Remove client packages assigned to the client groups
4) Enable local authentication
5) Stop the Symantec Endpoint Protection Manager service
6) Upgrade the Symantec Endpoint Protection Manager
6) Enable replication after upgrading
7) Upgrade the Symantec Endpoint Protection clients
This article can help you to find more details on above points: http://www.symantec.com/docs/TECH224034
System requirements are also important to know, check here: http://www.symantec.com/docs/TECH224712
To know the best practice I would recommend you to go through the following article.
https://www-secure.symantec.com/connect/articles/sep-11x-sep-121-upgrade-process-graphical-overview
Important note: The SEP 12.1 SEPM upgrade installer requires three times the current database size (sem5.db) if upgrading from pre-12.1 SEPM with the embedded database only.
Reference : http://www.symantec.com/docs/TECH162730
Auto upgrade can be easiest way to upgrade existing clients.
FAQ: Upgrading Symantec Endpoint Protection 11.x to version 12.1.x
http://www.symantec.com/docs/TECH207274
Q,.Should i have to uninstall 11.x or can migration can be possible ?
--> Migration of 11 clients to 12.1 is also supported. Reboot is required to complete the upgrade. Reboot is required because SEP 12.1 employs a side-by-side, replace on reboot installation strategy. Side-by-side means that new files are written to a new folder, referred to as a silo, isolated from the existing operational folder. Because the two versions are separated from each other, during a migration the older software is left running unchanged until the next reboot.
The primary benefit of side-by-side installation and replace on reboot is that the system continues to be protected by the existing software until the new version is in operation after the reboot.
This technique enables you to change the normal portion of the installation path during a migration, when applicable.
Q. Some Machines are running on Windows XP Still , yes we love XP still.
--> Symantec is committed to providing the best possible security for its customers. Even as Microsoft stops publishing new functionality and security updates for Windows XP in 2014, Symantec will continue to release 32-bit and 64-bit definition sets that are compatible across all 32-bit and 64-bit Windows platforms supported by the product.
While we encourage our customers to follow best practice security procedures and update their systems to more secure operating systems when possible, Symantec will continue to release antivirus definitions and product updates compatible with Windows XP for the current product cycle.
Check this article for more info: How Windows XP end of support affects Endpoint Protection.
http://www.symantec.com/docs/TECH204937
If you need any assistance with an upgrade feel free to PM me. :)